Annunciator system with acknowledgment and reset



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June 9, 1964 .1. SARGENT 3,136,982

ANNUNCIATOR SYSTEM WITH ACKNOWLEDGMENT AND RESET Filed Sept. 19, 1960 4Sheets-Sheet 4 United States Patent O f 3,136,982 ANNUNSIATR SYSTEM WliiACKNOWLEDG- Y MENT AND RESET Back Sargent, Chicago, lll., assigner, bymesne assignments, to Scam instrument Corporation, Skokie, iii., a

corporation of illinois l Filed Sept. 19, 1966, Ser. No. 56,396 8Claims.v (Cl. S40-413.1)

` This :invention relates to annunciator systems of the type wherein avisual alarm unit, such as a light unit, is provided for each variableto be monitored, and, when the variable becomes abnormal, a pair offield contacts are actuated to operate the visual alarm unit whichindicates that the variable involved has just become abnormal. Amanually operable acknowledgement switch is usually provided, which,when operated, changes the indication of the visual alarm unit toindicate that the alarm has been acknowledged by the operator. Usually,an audible alarm is also included to attract the operators attention toa central control panel containing the visual alarm units associatedwith practically all of the variables to bemonitored in the plantinvolved, so that the operator can determine at a glance the conditionof all of the variables.

For the most part, annunciator systems of the kind just described haveheretofore been hydraulically or relay controlled systems, and thesesystems left much to be desired from the standpoint of reliabilitybecause of mechanical wear and, in the case of the relays, additionallybecause the relay coils sometimes burned out. Obviously, it is quiteimportant for annunciator systems to be reliable, since otherwise, theycould not fulll their intended purpose. More recently, static controlelements, such as magnetic cores, have been used in annunicator systemsto replace relays to provide a system of improved reliability. Suchannunciator systems have also been recently developed operating withtransistor control elements.

Although the annunciator systems have proven satisfactoryV for manypurposes, they have certain drawbacks overcome bythe present invention.For example, magnetic core as well as transistor annunciator systemshave required special Ypower supplies. The provision of special powersupplies not only increases the expense of the system but, moreimportantly, reduces materially the reliability of the system. Failureof a power supply will,

v lof course, result in breakdown of the entire system;

Transistors are generally operated from low voltage power supplies.Typical voltage limitations of transistorsare volts for the more common,economical transistors and 45 and 85 volts for the more expensive andless cornmon types. Low voltage operation means high currentrequirements in transistor `circuits controlling light sources and thelike. For. example, in the case of a 4 or 5 watt lamp, the currentrequired for a single lamp is frequently in the order of 1/2 of anampere. Where a large number of points `are being monitored by theannunciator system, the potential current requirements where a largenumber of variables are simultaneously abnormal can be quite high.VProblems of overheating of certain v components in the power supplycarrying common load current, and providing good regulation where loadre-` quirements vary widely as in the case of annunciator systems createexceedingly difficult problems.

Particular ditiiculty has been encountered in providing Y staticannunciator systems for monitoring power stations.

Power stations commonly have a 125 volt D.C. battery` supply source forthe control circuits which operate the power station. These controlcircuits have generally been relay systems which operate readily at suchvoltages. To operatev static annunciator systems from such a powersource has heretofore required special converters for pro- 3,136,982Patented .lune 9, 1964 ice viding the necessary voltages for operatingthe static control elements involved. In the case of annunciators usingtransistors, Ythe required low voltage lcould not satisfactorily besupplied by merely adding a common resistor voltage` dividercircuitsince this voltage divider must be able to carry a high andwidely varying current where the aforesaid overheating and regulationproblems would obviously bel present. Prior to the present invention itwas believed necessary to utilize either a motor generator converterwhich converted the relatively high direct current battery supplyVoltage directly to a low direct current voltage, or a vibrator whichconverted the battery voltage. to pulsating or alternating current whichwas fed through a transformer to provide the necessary low voltage. Theuse of these converters provide cost, reliability and, to a lesser butnonethelesssigniiicant extent, lregulation problems. l

Itis, accordingly, one of the objects of the invention to provide astatic element annunciator system, preferably a transistor annunciatorsystem, which is capable of y operating directly from a 125 volt directcurrent voltage source, such as the battery supply commonly found inpower stations. i

Many of the static annunciator systems heretofore developed usedflip-Hop (bistable) circuits as basic control elements. These bistablecircuits frequently operated from capacitor pulse-forming networks inturn controlled by eld contacts controlled directly by the variablesinvolved. The reliability of these annunciator systems were sometimesadversely affected by the presence of large distributed capacity in thelines where long distances separated the iield contacts from thepulse-forming net' works.

Another one of the objects of the invention, therefore, is to provide astaticV element annunciator `system utilizing. bistable circuits wherethe distributed capacity of long lines interconnecting the tieldcontacts withthe` associated bistable control .circuits do not adverselyaffect the operation of the bistable circuits.

In accordance with one aspect of the invention, there is associated witheach variable to be monitored a bistable circuit including a pair oftransistor control elements each having a pair of load terminalscommonly referred to as emitter and collector electrodes and a controlterminal commonly referredV to as a base electrode. Where type PNPtransistors are utilized, a resistor is connected between the collectorelectrode of each transistor and the negative terminal of the highdirect current voltage source whose magnitude is many times greater thanthat of the applied voltage source for which the transistors aredesigned to operate. The emitter electrode thereof is connected to theother terminal of the direct current voltage source. A resistor isconnected between the collector electrode of each transistor and thebase electrode of the other transistor forming the associated bistablecontrol circuit. Another resistor is connected between each baseelectrode and the positive terminal of the direct current voltagesource. The values of the aforementioned resistorsare so proportionedthat they effectively act as a voltage divider which reduces the voltageat the collector electrodes to a low value to which the transistors arenormally designed toV operate. It is apparent that none ofthe resistorsreferred to carry any substantial current since they only carry thecurrent required for the associated bistable circuit. Thus, nooverheating or regulation problems are involved as would be the case ifa common voltage divider network were to be utilized to drop the voltageof the source of direct current voltage to the proper value. annunciatorcircuit are similarly operated from the high voltage direct currentvoltagesource.

The other transistors of the Various types of relay aununciator systemshave become popular in recent years. In one type, the visual and audiblealarm signals for a momentary abnormal variable are locked-in so thatthe alarm information is preserved until a record of the momentarytrouble is made. Another type is referred to as a non-lock-in systemwhere the visual and audible alarm signals for a momentary alarm are notmaintained. `The lock-in type of annunciator system, in addition tohaving a manual acknowledgement switch for silencing the audible signaland, in many cases, changing the initial visual indication involved to adifferent acknowledged indication, includes a manual reset switch forterminating the visual signal when the variable returns to normal afteracknowledgement, This is referred to as a manual reset feature.Annunciator systems made with static elements, particularly transistors,have offered some but not all of these features. For example, there is aneed for transistorized annunciator systems which provides in a simpleand reliable manner a selection of lock-in and non-lock-in operation,and/ or a selection of manual reset and automatic reset operation afteracknowledgement.

It is, accordingly, an object of the present invention to provide areliable static element annunciator system, providing for a selection ofnon-lock-in and lock-in operation, and/or manual reset and automaticreset operation. Y

In accordance with another aspect of the present invention, each set offield contacts is arranged to feed a continuous set signal to one of thecontrol terminals of the associated bistable circuit. Where transistorsare used as the static elements in the bistable circuit, the set signalis a direct current potential. A unique reset circuit is associated withanother control terminal of the bistable circuit which continuouslyprepares the bistable circuit for a reset operation which becomeseffective when the set signal is removed bythe return of the variableinvolved to normal. This arrangement results in a fast acting bistablecircuit which is not adversely affected by the distributed capacitancein the long lines connecting remotely located field contacts to theannunciator circuit. Such capacitance could slow down the response of abistable circuit responding to a pulse generated by operation of thefield contacts to a point where an abnormal variable would not bedetected. The reset circuit preferably includes a source of reset pulseswhich are continuously coupled to the reset control terminal of thebistable circuit so that a reset operation may occur substantiallyimmediately after the field contacts return to their normal condition todisconnect the aforementioned set signal from the bistable circuit.Connections are made from the bistable control circuit to an associatedvisual alarm control circuit so that the alarm light becomesde-energized as soon as the variable returns Ito normal. This is thenon-lock-in operation referred toy above. If it is desired to lock-in aninitial alarm indication of the variable (which might be abnormal onlymomentarily), a manual select switch may be provided to de-couple orinhibit the effect of the reset pulses. In the preferred form of theinvention, a second bistable circuit is provided for each variable whichis initially set by the initial triggering of the first-mentionedbistable circuit, the set condition thereof inhibiting the effect ofsaid reset pulses on the first bistable circuit until reset by operationof a manually operable acknowledgement switch. The acknowledgementswitch in such case may be properly called a reset switch (and isreferred to as such in some of the claims herein). The aforementionedmanual Vselect switch is used to selectively couple and uncouple theinhibit output of the second bistable circuit to provide for a selectionof lock-in or non-lock-in operation.

Where manual reset operation is desired, the aforesaid source ofcontinuous reset pulses may be removed from the circuit or de-coupledtherefrom, and a manual reset switch added to the circuit which resetsthe first-mentioned CTL l bistable circuit after the reset inhibiteffect of the second bistable circuit is terminated by operation of theacknowledgement switch. Removal of the continuous reset pulses provideslock-in after acknowledgement.

Other objects, advantages and features of the invention will becomeapparent upon making reference to the specification to follow, theclaims and the drawings wherein:

FIG. 1 is a schematic diagram of a transistorized annunciator system ofthe invention providing a simple nonliashingvisual alarm sequence;

FIG. 1a shows a printed circuit card which holds the circuit componentsexclusive to a single variable;

FIG. 2 is a table illustrating the various conditions of operation ofthe annunciator system of FIG. l;

FIG. 3 is a simplified box diagram of another annunciator systemproviding a flashing visual sequence and a selection of lock-in andnon-lock-in operation;

FIGS. 4 and 5 are a schematic diagram of a preferred transistorizerembodiment of the annunciator system shown in FIG. 3;

FIG. 6 is a table illustrating the conditions of operation of thecircuit of FIGS. 4 and 5; and

FIG. 7 illustrates a minor modification of the circuit of FIGS. 4 and 5which provide for an optional manual reset operation.

N ort-F lashing Transstorzed Annunciqtor System The annunciator systemshown in FIG. l is made of PNP type transistors, resistors, diodes andcapacitors forming a light control circuit comprising a signal inputcircuit 2, a bistable circuit 4 and a light amplifier circuit 6associated with each variable; A horn control circuit 7 is providedcomprising a bistable circuit l0 and a horn amplifier circuit 12 incommon with all variables. The light control circuits exclusive to thevariables (only one of which appears in FIG. l) are connected inparallel between various buses generally indicated by reference numeral13. Most of the components making up each control circuit are placed ona single printed circuit card 14 shown in FIG. la which can be mountedin plugin relation to connectors mounted on a common frame. The commonhorn circuits 10 and 12 can be mounted on a similar printed circuit cardnot shown. Each light control circuit controls the operation of an alarmlamp L and the horn circuits control a horn H.

Before discussing the annunciator system in detail, it would be helpfulto review the basic sequence of operation of each alarm lamp and horn.When a particular variable goes abnormal, the associated alarm lamp L isoperated to a steady bright condition and the common horn H is sounded.A manually operable acknowledgement switch 14 is provided in common withall of the control circuits and, when momentarily depressed, silencesthe horn H. A common manually operable reset switch 16 is also providedwhich, When momentarily operated, extinguishes the alarm lamp L only ifthe associated variable has returned to normal.

In accordance with one aspect of the invention, substantially all of thetransistors used vin the annunciator circuit are low (e.g., 25 volts)voltage transistors arranged in a unique circuit to be described wherethey are operated directly from a relatively high direct current voltagesource 20, suchas volts commonly found in direct current battery supplysystems of power stations.

The condition of the basic variable being monitored is identified vbythe position of a set of field contacts 22 (which may be bi-metaltemperature responsive contacts in the case of a temperature variable,bellow-operated contacts in the case of a pressure variable, etc.)located at the situs of the vvariable involved. Each set of eld contactsV22, which are illustrated as normally-opened contacts which are closedwhen the associated variable becomes abnormal, are usually connected bylong conductors 23 to connecting terminals 24 of the signalinmally-closed set of lield contacts 22 connected through longconductors to connecting terminals 25, which contacts maybe substitutedfor the normally-open contacts. When operating with normally-open eldcontacts, a jumper 26 is connected between the terminals 25. The upperof the terminals 25 is connected to ar common negative voltage bus 28leading to the negative terminal of the battery source 20. The bottomterminal 25 ex- Vtends through a resistor 30 to the upper field contactconnecting terminal 24. The bottom field contact conv necting terminalis connected to a common grounded bus 34 leading to the positiveterminal of the battery Y source 20. A resistor 35 is connected betweenthe terminals 24. The signal input circuit further includes a filternetwork comprising a resistor 42 connected between resistors 30 and 36and capacitor 44 connected to the common ground bus 34. -The filternetwork further includes a resistor 46 connected between the juncture ofresistor 42 and filter capacitor 44 anda resistor 48 connected to theground bus 34. The filter network bypasses sharp noise impulses whichmay be picked up in the field conductors 23 which could initiate a falsealarm.

The value of lter capacitor 44 depends, in part, upon a consideration ofthe minimum switch closure time which the annunciator circuit is torespondand the length of the line extending between the eld contacts andthe signal input circuit. FIG. 1 shows alock-in circuit which holdsalarm signals for momentary abnormal variables where the field contactsmay close for a period of only 700 micro-seconds (or longer). This meansthat the time constant of the signal input circuit must be suflicientlyshort that a 700-micro-second closure time will v result in actuation ofthe control circuit. A 400 microL `ln some instances, the customer maydesirerto control some auxiliary device directly from the fieldcontacts, and, accordingly, a control coil (not shown) may be placed inseries or parallel with the eld contacts. The presence of a relay coilin the signal input circuit could result in the generation of largepositive voltage spikes when current is suddenly interrupted in therelay coil which could damage a transistor T3 connected in the signalinput circuit. To prevent the coupling of these voltage spikes to thetransistor T3, a diode t) is connected across resistor 48 to shortcircuit any positive voltage pulses to ground. The upper terminal ofresistor 48 is connected to the control terminal or base electrode 52 oftransistor T3.

"The closure of the normally-open field contacts 212 (or the opening ofthe normally-closed contacts 22') results in the application of positiveor ground petential to the input of the signal input circuit. Thispotential appears at the base electrode 52 to render the samenonconductive.

The transistor T3 is a low voltage PNP junction tran sistor whoseemitter electrode 54 is connected to a bias.- ing silicon diode 56 inturn connected to the common ground bus 34. VThe diode 56 is connectedto offer a Y low impedance path for` normal transistor current flow.

' The diode 'V56 may, forV example, provide a 1/2 volt bias fortransistor T3 and othery transistors to which lit is connected. Thecollector electrode 56 of the transistor T3 is connected to a loadresistor 58 in turn connected to the common negative voltage bus 2S.Y

The low voltage transistor T3 (as well as most of the other transistorsof the annunciator circuitlmay be a Motorola type 2Nll9l having a 25volt emitter to collector voltage rating.y A resistor 6i) and a resistor62 are accordingly connected in series between the collector electrode56 and the common ground bus 34. The Values of resistors 58, 60 and 62are so proportioned that when the transistor T3 is non-conductive, thevoltage at the collector electrode is less than 25 volts. Typical value.of these resistors may be as follows: j,

The ratio of the value of resistor 58 to resistors 62 and 60 isexceedingly higher than is normally found in transistor circuits sinceone of the main functions of resistor 58 is to drop the high directcurrent voltage (-l25 v.) to less than 25 volts. It is signiiicant thatin the use of transistors inv annunciator systems that no one prior tothe present invention has modified the usual resistor value ratios toadapt the transistors for use with high direct current voltage supplysources such as is commonly available in power stations and thelike.

Rather, as above explained, the prior art has resorted to more costlyand less reliable converters.

The transistor T3 and the associated resistors form a voltage inversioncircuit for providing the proper control voltage conditions for theHip-iop or bistable circuit 4.

The bistable circuit 4 comprises a pair of PNP transistors T4 and T5like transistors T3 having two control input terminals 63 and (4.` Thecontrol input terminal 62 is at the juncture of resistors 6i) and 62which is connected to the base electrode 66 of the transistor T4. Thecollector electrode 68 of `transistor T4 is connected through a resistor7i) to the common negative Voltage.

bus 28. The emitter electrode 72 of transistor T4 is connected to acommon bias line 76 leading tothe upper terminal of the biasing diode56.

The other transistor T5 of the bistable circuit has its base electrode78 connected to the control input terminal 64. The transistor T5 has itsbase electrode 78 connected to the common biasing line 76 extending tothe biasing diode 56. A resistor 80 extends between the control inputterminal 64 and the common ground bus 34. A resistor 82 is connectedbetween the control input tertminal 64 and the collector electrode 66 ofthe transistor T4. Y A resistor S4 is connected between the collectorelectrode S6 of the transistor T5 and the common negative Voltage bus2S. A resistor 8S is connected between the collector electrode 86 oftransistor T5 and the control input terminal 63 associated with the baseelectrode 66 of the transistor T4. The resistors 82 and 8S`are thuslocated in feed-back branches extending from the outputs of therespective transistors T4 and TS tothe control electrodes of the otherof same to thereby provide a bistable or flip-flop circuit action lnVaccordance with the present invention these resistors, however, performan Y added important function in cooperation with resistor pairs 7th- 89and 84-62 which is to reduce the negative volts applied voltages to alow voltage (below 25 volts) applied across the collector and baseelectrodes of transistors T4 and T5. Typical values for the resistors ofthe bistable control circuit just described are as follows:

R70 and R74100,000 ohms R62 and R80-4,700 ohms RSZ-7,000 ohmsRSS-,22,000 ohms Initially, transistor T3 is in a relatively highconductive state due to the presence of a negative potential on its baseelectrode 52. In this state, the collector electrode 56 of transistor T3is near ground potential which renders the left hand transistor T4 ofbistable circuit 4 non-conductive which, in turn, makes the right handtransistor T5 thereof `normally conductive. When field contacts 22 closeto render transistor T3 non-conductive in the manner described above,the resulting negative potential appearing on the collector electrode 56forces bistable transistor T4 into conduction which, in turn, rendersbistable transistor T5 non-conductive.

The bistable circuit 4 may also be set into the conductive state justdescribed by closure of a manually operable test push-button switch S5connected between common test bus 87 and the negative voltage bus 28.The control input terminal 63 or base electrode 66 of each controlcircuit 1 is connected to the test bus. Depression of the test switchwill test the operation of the annunciator by creating identical signalconditions as closure of contacts 22.

The bistable circuit 4 can be reset to its normal stable state by thereset switch 16 provided the field contacts 22 are re-opened. The resetswitch 16 is connected between a common reset bus 89 and the negativevoltage bus 28. When the reset switch is momentarily depressed, anegative potential is coupled to the base electrode 78 of the transistorT5 to effect a high conductive state thereof. This will result in theoperation of the left hand transistors T4 to a relatively non-conductivestate.

Before the variable associated with the control circuit now beingdescribed goes abnormal, the left hand transistor T4 thereof isnon-conductive and the potential of the collector electrode 63 thereofwill be negative. A capacitor 90 is connected between the collectorelectrode 68 and a resistor 91 connected to the ground bus 34. Thecapacitor 90 initially charges to the negative potential on thecollector electrode through the resistor 91. When the varaible goesabnormal and the bistable circuit 4 is triggered into a state wheretransistor T4 is conductive, the voltage at the collector electrode 68is near ground potential which eiects the discharge of the capacitor 90through the resistor 91. A positive pulse is thereby generated acrossthe resistor 91. The capacitor 90 and the resistor 91 eifectively formwhat is commonly referred to as a differentiating network. This positivepulse is coupled through a resistor 92 and an isolating rectier 93connected to pass positive pulses to a common horn bus 94 which connectswith the horn bistable circuit 10. The horn bistable circuit istriggered into a state which effects energization of the horn H in amanner to be explained.

The aforesaid drop in potential at the collector electrode 68 oftransistor T4 is coupled through a resistor 102 to the base electrode104 of a low voltage, low power PNP junction type control transistor T1.A resistor 105 is connected between the base electrode 104 and theground bus 34. The collector electrode 106 of the transistor T1 isconnected through a resistor 108 to the negative voltage bus 2S. Theemitter electrode 110 of the transistor T1 is connected through abiasing diode 112 to the ground bus 34.

Transistor T1 controls the operation of a high voltage PNP junctiontransistor T2 which, for example, may be a general transistor type GT1402 having a rating of 85 volts. A high Voltage transistor is expensiverelative to low voltage transistors and is used here because the loadcircuit thereof includes the lamp L which has a much lower voltagerating. The base electrode 111 of this transistor is connected to thecollector electrode 106 of the transistor T1. The emitter electrode 113of the transistor T2 is connected by a silicon biasing diode 115 to theupper terminal of the biasing diode 112 and by a resistor 122 to thenegative voltage bus 28. The collector electrode 117 of the transistorT2 is connected through the lamp L to the negative voltage bus 2S. Aresistor 119 is connected between the collector electrode 117 and theground bus 34. This resistor 119 drops the voltage across the transistorto volts when it is nonconductive and allows sufficient current to iowthrough the lamp L to light the same dimly. In the case where the lamp Lis a 6 watt lamp, the resistor 119 may be a 3300 ohm 4 watt resistor.

Under normal operating conditions of the control circuit where the lefthand transistor T4 of bistable circuit 4 is non-conductive, a negativepotential is coupled through the resistor 102 to the base electrode 104of transistor T1 which renders the same highly conductive. When theassociated variable goes abnormal and the bistable transistor istriggered into a highly conductive state, a potential near groundpotential is fed to the base electrode 104 of transistor T1 to renderthe same non-conductive.

When transistor T1 is conductive during normal operation of the controlcircuit 1, this condition will provide something less than l voltnegative at the base electrode 111 of the transistor T2. The combinationof the two diodes 112 and 115 connected in series with the emitterelectrode 113 of transistor T2 and resistor 122 provides a voltage inthe neighborhood of l volt at the emitter electrode 113, so that thebase electrode of transistor T2 is positive with respect to the emitterelectrode, thereby rendering the transistor T2 non-conductive. When thevariable involved goes abnormal, and the transistor T1 accordinglybecomes non-conductive, a negative potential appears at the baseelectrode 11 of power transistor T2 thereby rendering the lattertransistor highly conductive to light the lamp L brightly. The emitterto base voltage when transistor T2 conducts is quite low (.5 volt) sothat the voltage at the collector electrode of transistor T1 is wellbelow 25 volts. The operating conditions of the light amplier circuitare returned to their normal state where light 6 is dimly lit when thebistable circuit 4 is reset by operation of reset switch 16 (when thevariable returns to normal in the manner previously explained).

As previously indicated, when any variable in the system goes abnormal,a positive voltage pulse appears on the horn bus 94 capable oftriggering a horn bistable circuit 10. The bistable circuit 10 issimilar to the light bistable circuit 4 previously described in detailso that the details of the circuit 10 will not be described. It issuicient to say that bistable circuit 10 has transistors T1 and T2 ofthe same low power type as the low voltage, low power transistorsTl andT2. The left hand transistor T1 is normally conductive and the righthand transistor T2 is normally non-conductive. Also the horn bistablecircuit includes load resistors 70 and 84', feedback resistors 82 and88', and control circuit resistors 62 and 80 which are so proportionedthat the voltage applied between the collector and emitter electrodes oftransistors T1' and T2 never exceed the rated value of the low voltagetransistors, which, for example, is approximately 25 volts.

The horn bistable circuit 10 has two control signal inputs bothextending to the base electrode of the transistor T1. One of theseinputs includes a resistor 127 extending from a common acknowledgementbus 129 to the base electrode 125. The other input includes a resistor131 extending from the common horn bus 94 to the base electrode 125. Theacknowledgement bus 129 is connected to the negative Voltage bus 2Sthrough a normally-open manually operable pushbutton switch 14. When oneof the variables in the system becomes abnormal and the horn bus 94 isaccordingly pulsed with a positive voltage, this potential fed to thebase electrode 125 renders the transistor T1 non-conductive and thetransistor T2 conductive. When the acknowledgement switch 14 ismomentarily depressed,`negative potential is coupled to the baseelectrode 125 which results in the return a ground clamping 9 of thetransistor T1 to a conductive state and the other transistor T2' to anon-conductive state.

A control voltage is coupled from the horn bistable circuit 10 toa pairof resistors 134 and 136 connected in series between the collectorelectrode 13? of the right hand transistor T2 and the ground bus 34. Aconnection 149 extends from the juncture of resistors 134 and 136 to thebase electrode 142 of a low voltage, low power, PNP junction transistorT3 located in the horn ampliiier circuit 12. Theemitter electrode 144 ofthe transistor T3 is connected to a biasing diode 146 in turn connectedto the ground bus 34. The collector electrode 146 thereof is connectedthrough a pair ot series connected` resistors 148 and 159 to thenegative power bus 12S. A connection 152 is made between the collectorelectrode 146 of transistor T3 and the base electrode 154 vof a highvoltage (S volts) power transistor T5. The

emitter electrode 156 of the transistor T5 is connected through abiasing diode 158 to the upper terminal of theV other biasing diode 146.Proper biasing voltage conditions are obtained for the transistor T5 bya pair of "resistors 160 and 162 connected in series between the'negative voltage bus 28 and the upper terminal of the biasing diode158. A connection 164 is made between the juncture of resistors 16,0 and162 and the collector electrode 156 of transistor TS.

f The load circuit kvof transistor 154 includes a power transistor T4'which is identical to transistor T5 and the horn 11 connected tothenegative voltage bus 28. The emitter electrode 165 of the transistor T4is connected to the collector electrode 166 of transistor T5. The baseelectrode 167 of the transistor T4 is connected through a resistor 169to the juncture of resistors 150 and 148. The collector electrode 171 ofthe transistor T 4 is connected to the horn. To protect the transistorsagainst reverse voltage spikes which may be developed in the circuit dueto the inductive kick in the coil of the horn 11, diode 173 is connectedbetween the juncture of the horn 11 and the collector electrode 171 voftransistor T4 and the ground bus 34 so as to bypass positive pulsesgenerated in the horn coil.

The transistor T3 is normally in a conductive state, and when the hornbistable circuit is triggered by the positive pulse on the horn bus 94to render the right hand transistor T2' conductive, this results in thecoupling of a near ground potential to the base electrode 142 of thenormally-conductive transistor T3' to render the same non-conductive.This, in turn, creates voltage conditions which eliect the conduction ofthe transistor T4 and T5' to energize the horn. When the acknowledgementswitch 14 is momentarily depressed to reset the bistable circuit 10, thevoltage conditions in the horn ampliiier circuit are reversed to renderthe transistors T4' and T5 non-conductive to de-energize the horn.

The Optional Abnormal Lock-In and Non-Lock-In Annunciatory System ofFIGS. 3 Through 6 Refer now particularly to FlG. 3 which illustrates abasic box diagram of an embodiment of the present invention providingoptional and lock-in and non-lock-in operation. In accordance with thebroadest aspects of this form of the invention, the various controlcircuits 1 connected in parallel across the buses 13, 94, 193 and 28 maybe made of any type of static components including, for example,magnetic core control elements Vand the like. This circuit may includenormally open (or normally closed) field contacts 22 associated with asignal input circuit 2 and a bistable circuit 4. When the lield contacts`22.2 are moved to their abnormal variable indicating position, acontinuous control voltage is coupled through the signal input circuit 2to a control input terminal 66 of the bistable circuit 4 to set the sameinto one of its two possible output conditions. The bistable circuit 4has another control input terminal '78 which is effective to reset thebistable circuit upon receiving a pulse of a given polarity as, forexample, a negative pulse. When the bistable circuit 4 is initially setby the control voltage at the control input terminal 66, an output line69 connects a source of relatively positive potential to adifferentiating network comprised by capacitor 90 and resister 96 andalso to one of the inputs 130V of a light control and gate 1&1 and oneof the inputs 182 of a horn control and gate 134. The and gates 131 and184 respectively have second inputs 187 and 189. In the circuitillustrated, if positive (ground) potential is present simultaneously onboth of the inputs of either and gate, the associated light L or horn Hwill be energized. The second input 187 of the light control and gate181 extends through a rectifier 191, arranged to pass positive (ground)potential from a common tiasher bus 193. A ilashing unit 195 common toall of the control circuits is connected between the liasher bus 193 andground potential which will be assumed to be positive with respect tothe other reference potential to be described, which is negative. Theiiasher 195 continuously feeds positive pulses` at a visible pulserepetition rate to the asher bus 193. lt is apparent when the bistablecircuit 4 is initially set by the movement of the field contacts 22 toan abnormal variable indicating condition that the light control andgate 181 will have simultaneous positive voltage inputs occurring at avisible ashing rate. Accordingly, the associated light L will beenergized at a visible liashing rate.

When the associated variable initially becomes abnormal, the aforesaidpositive voltage fed to the differentiating network comprising capacitor96 and resistor96 generates a momentary positive pulse across resistor96 which is coupled through a diode 299 (connected to block negativepulses generated by the discharging of capacitors 90) to the controlinput terminal 78' of a bistable circuit 4 which is similar to thebistable circuit 4. This positive pulse sets the bistable circuit 4 intoone of two positive output conditions. An output line 194 extends fromthe bistable circuit 4 to the input 187 of the light control and gate181. The output line 194 and the connection of the rectifier 191extending from the asher bus 193 to the input 187` constitutes an orconnection. The voltage on the output line 194 of the bistable circuit 4has a negative potential when the bistable circuit 4 is initially setwhen the associated variable becomes abnormal, and a positive potentialwhen the bistable circuit 4 is reset. Reset of this bistable circuit isobtained by the momentary depression of acknowledgement pushbuttonswitch 14 which connects a source of negative potential from negativebus 28 to the control input terminal '7S' of thebistable circuit 4'. Theresulting continuous positive voltage on the output line 194 fed to theand gate input 187 Vwill, in conjunction with the continuous positiveVoltage fed to the input 180 thereof from the output line 69 of on theassociated output line 194 whereby the output terminal 199 has arelatively negative potential when the associated bistable circuit isset in response to the abnormality of the associated variable and has arelatively positive potentialfwhen the bistable circuit is reset byoperation of the acknowledgement switch 14. When the associated variableinitially becomes abnormal, the two inputs 182 and 139 of the horncontrol and gate 184 will respectively have a positive potential appliedthereto from bistable output line 69 of bistable circuit 4 and outlineline 201) connected to output terminal 199. In the particular circuitbeing described, this will result in the feeding of negative potentialfrom the negative bus 2S to the common horn bus 94. The negativepotentialon the horn bus 94 is fed to the input terminal 202 of a commonhorn ampliier circuit 203 which will energize the associated horn H.

As previously indicated, the annunciator circuit now being describedprovides for optional non-lock-in and lock-in operation. To this end, amanual switch 206 is provide having a movable contact 208 selectivelyengageable with stationary contact Nos. 1 or 2. When the movable contactis in position No. 1, the circuit provides nonlock-in operation wherethe condition of the lamp L follows the position of the iield contacts22, and when it is in position No. 2 it provides a lock-in operationwhere momentary abnormal variables will be indicated by an indication onlamp L which can only be removed by operation of the manualacknowledgement switch 14.V To effect de-energization of the lamp L itis necessary to reset the bistable circuit 4. In the embodiment of theinvention now being described, a unique reset circuit for the bistablecircuit is provided which most advantageously includes a seriesnconnected resistor 211 and 211' connected between the negative voltagebus 28 and ground, a capacitor 212 connected between resistor 211 and aresistor 214 connected to ground. A rectifier 216 is connected betweenthe juncture of capacitor 212 and resistor 211 and the flasher bus 193.As previously indicated, the asher bus 193 is pulsed with positive (orground) pulses at a visible fiashing rate. When a positive (or ground)pulse appears on the bus 193, this effectively provides a short circuitbetween the upper capacitor plate and ground which causes the capacitor212 to discharge through resistor 214 providing a positive pulsethereacross. The ungrounded end of resistor 214 is connected through arectifier 218 to the control input terminal 7S of the bistable circuit4. The rectifier 21S blocks the positive pulses developed across theresistor 214. However, upon momentary disappearance of a positive pulsefrom the fiasher bus 193, the capacitor 212 recharges to a negativevoltage which provides a negative pulse across the resistor 214. Thispulse passes through rectifier 213 to trigger the bistable circuit 4provided the aforementioned control voltage fed to the other controlinput terminal of the bestable circuit 4 is removed by return of thefield contacts 22 to their normal variable indicating position. Untilthe latter control voltage is removed from the bistable circuit 4, thebistable circuit is effectively desensitized (i.e., incapable of beingreset).

Optional lock-in operation is provided by the connection of the outputterminal 199 of the bistable circuit 4 through a rectifier 213 connectedto pass only positive (or ground) potential, the No. 2 position ofswitch 206, and the movable contact 208 to the juncture between thecapacitor 212 and the rectifier 216 leading to the fiasher bus 193. Whenthe bistable circuit 4 is in a normal or reset condition, the outputterminal 199 has a negative potential blocked by the rectifier 213. Whenthe associated variable becomes abnormal, a positive (ground) potentialappears at output terminal 199, which is coupled through rectifier 213and switch 206 to the upper plate of capacitor 212 which discharges andmaintains it discharged until acknowledgement, which prevents reset ofthe bistable 4 by the pulsations on flasher bus 193. Afteracknowledgement, however, the potential of output terminal 199 becomesnegative again and thus has no effect on capacitor 212, so that thepulses then fed to the capacitor circuit from the flasher' bus 193 areeffected to generate the negative pulses across the resistor 214 whichcan reset the bistable circuit 4 when the associated variable returns tonormal.

Refer now to FIGS. 4 and 5 showing a preferred transistor embodiment ofthe annunciator system shown in FIG. 3. Many of the component parts ofthis circuit are substantially identical to that shown in FIG. land areidentified by similar reference characters. For example, the inputcircuit 40 in FIG. 4 is identical to input circuit 2 in FIG. l.Likewise, the bistable circuits 4 and 4', each are substantiallyidentical to the transistor bistable circuit 4 in the embodiment ofFIG. 1. Many of the interconnections of these circuits with the variousparts of the annunciator systems are, however, different and these willbe described in detail. The control input terminal 66 of bistablecircuit 4 in FIG. 3 is the base electrode of the left hand transistor T4and the control input terminal '78 shown therein is the base electrodeof the right hand transistor T5. The rectifier 218 is connected througha current-limiting resistor 223 to the base electrode 78 and the outputline 69 extends from the collector electrode of the left hand transistorT4. The control input terminal 78 of the bistable circuit 4 is the baseelectrode of the right hand transistor T5 and the rectifier4 209connected to the base electrode 78 is coupled through a resistor 224 tothe juncture of capacitor 90 and resistor 91. A voltage droppingresistor 219 is connected between the acknowledgement bus 129 and theline` leading to the base electrode 78'.

The input 180 to the and gate 181 is connected through a resistor 225 tothe base electrode 142 of a transistor T1 forming part of a lightcontrol circuit which, except for the and input connections, is similarto the circuit associated with transistor T1 in FIG. l, and thecorresponding elements thereof are similarly numbered. The input 187 tothe and gate 181 is connected through a resistor 228 to the baseelectrode 142 of the transistor T1. The exemplary values for resistors225 and 228 are 82,000 ohms and 33,000 ohms, respectively. Theresistance Values of the rest of the circuit associated with transistorT1 may be the same as that previously indicated for the correspondingcircuit in FIG. 1.

The output line 194 of the bistable circuit 4 is connected from thecollector electrode of the right hand bistable transistor T5 and througha resistor 230 (of an exemplary value of 47,000 ohms) to the input 187of and gate 181 at the juncture of rectifier 191 and resistor 228. Theimpedance relationships and circuit connections are such that thetransistor T1 will be conductive unless positive or ground potential issimultaneously applied to both inputs 180 and 187.

When transistor T1 is renderedv non-conductive, a high voltagetransistor T2 having a load circuit including the lamp L is renderedconductive to light the lamp L. The circuit associated with transistorT2 is substantially identical to the circuit of transistor T2 in theembodiment of FIG. 1 previouslyv described.

The control input terminal 182 of the horn control and gate 184 isconnected through ya resistor 231 to the base electrode 233 of a lowvoltage, low power transistor T8. This transistor TS and associatedcircuit has no counterpart in the embodiment of FIG. 1 and thus will nowbe'described in detail. The other control input terminal 189 of the andgate 184 is connected through a resistor 23S to the base electrode 233of the transistor T8. The collector electrode 233 of transistor T8 isconnected through a resistor 240 to the negative voltage bus 28 andthrough a resistor 242 and an isolating rectifier 244 arranged to coupleonly a negative voltage to the common horn bus 94. The emitterelectrode` 246 of transistor T8 is connected to the common bus line 76leading to the biasing diode 56 physically shown in FIG. 4 below theinput circuit transistor T3.

The manner in which the horn and gate operates is similar to light andgate 181. Thus, resistors 231 and 235 in relation with the otherresistors connected thereto provide a normally highly conductivecondition for transistor T8 when ground or positive potential is absentfrom either inputs terminals 187 or 189 and provides a nonconductivecondition of transistor T8 when positive potential is simultaneouslypresent at these input terminals. The non-conductive condition oftransistor T8 will result in the coupling of the negative potential ofthe negative voltage bus to the horn bus 94.

. As shown in FIG. 5, the horn bus 94 is connected through a resistor246 to the base electrode 248 of a low voltage, low power transistor T2forming part of an amplifier circuit resembling the bistable circuits 4and 4 28. The base electrodes 248 and 250 are respectively coupled totheground bus 34 through resistors 256 andV i 258. A voltage dividingresistor 261 (22,000 ohms) is connected between collector electrode 252and the emitter electrode 260 of transistor Tl, the latter electrode aswell as the emitter electrode 262 of transistor T2 being connected togroundy bus 34 through a biasing diode 263. The values of the variousresistors just described are y similar to the corresponding resistors ofthe bistable circuits 4 and 4.

When the variable goes abnormal and a negative pulse is fed to the hornbus 94 and thence to the base electrode 248 of transistor T2', thetransistor T2 is rendered conductive. (Initially this transistor isnon-conductive and the associated transistor T1 is conductive.) Whentransistor T2 is rendered conductive, the transistor T1 is madenon-conductive by the appearance of a near ground potential in its'baseelectrode due to the feedback path from the collector electrode 247 oftransistor T2 and through resistor 249. (The initial non-conductivestate of transistor T2 is due to the positive or ground potential on thehorn bus when all variables are normal.) The transistor T1 is actuallynot necessary to the operation of the circuit and is present primarilyfor standardizing on a printed circuit card which may be used for avariety fof diiierentcircuit arrangements as, for example, that shown inFIG. l.

As indicated in adescription of FIG. 3, the provision of and gatecircuit 184 controlling operation of the circuit makes it unnecessary toutilize a bistable circuit to control the horn H.

When the manually operable acknowledgement switch 14 is depressed andthe bistable circuit 4' is reset causing the closing of and gate 184indicated by the conduction of transistor T8, ground potential is fed tothe horn bus and thence to the base electrode of transistor T2 to renderthe same non-conductive; The non-conductive state of transistor T2 willresult in the de-energization of therhorn H. p Y

The collector electrode 247 is coupled through load resistors 264 and265 to a loW voltage, low power transistor T3' forming part of a circuit12 which is identical to the circuit 12 associated with the similarlyidentified transistor in FIG. 1. Thus, when the transistor T2 isinitially in a non-conductive state, a negative voltage is coupled tothe base electrode 142 of transistor T3 to render the same conductive.In a manner previously described, this effects a non-conductive state inthe series connected high voltage power transistors T4!` andTS whichprevents energization of the horn H. When the transistor T2 becomesconductive, the potential coupled to the base electrode of thetransistor T3' will be near ground potential to invert the states ofconduction of the transistors T3', T4 and T5to effect energization ofthe horn 11.

The flasher circuit 195 is shown in FIG. 5 and it includes a pair oftransistors T and T11 arranged to form a multivibrator circuit having apulse repetition rate, for example, of in the order of one cycle asecond. The multivibrator circuitrincludes a resistor 275 connectedbetween the collector electrode of they transistor T10 and a line 277coupled to the negative voltage bus 28 through a voltage droppingresistor 279. A resistor 231 extends from the collector electrode of thetransistor T11 to the line 277. The emitter electrodes of both of thetransistors T11? and T11 are connected directly tothe ground bus 34. Thebase electrode of the transistor T10 is coupled through a resistor 284tothe line 277 and the base electrode of transistor T11 is connectedthrough a resistor 286 to the line 277. A capacitor 287 is'cou- Y 14pled between the collector electrode of transistor T19 and the baseelectrode of transistor T11. Similarly, a capacitor 288 isv coupled fromthe collector electrode of the transistor T11 to the base` electrode oftransistor T10. Thecapacitors 288 and 287 in conjunction with associatedresistors form timing networks which establish the pulse repetition rateof the multivibrator circuit.

The output of the multivibrator circuit is taken from Vthe collectorelectrode of the transistor T10. A resistor 290 is accordingly coupledbetween the collector electrode of transistor T10 and the base electrodeof a transistor T9. A resistor 292 is connected between the baseelectrode of the transistorA T9 and the ground bus 34. A biasingresistor 294 is connected between the line 277 and the emitter electrodeof transistor T9. A biasing diode 296 is connected between the emitterelectrode of the latter transistor and the ground bus 34. The voltage atthe collector electrode of the multivibrator transistor T10 variesbetween ground and negative potential. It is apparent that when thispotential is at ground, the transistor T9 whose base electrode receivesbiasing voltage from the collector electrode of transistor T10 will bein a non-conduotive state. When the voltage coupled from the lattercollector electrode is'negative, this will result in the conduction oftransistor T9 whose load circuit extends to the aforementioned asher bus193. The flasher bus, in turn, as above indicated extends through thevarious control circuits of the annunciator system to the negativevoltage bus 28.

The flexibility of the annunciator system of FIGS. 3 thnough 5 is sosubstantial that it may readily be converted to an annunciator systemproviding an optional manual reset. As above indicated, a manual. resettype of operation is one wherein a visual indication is maintained onthe lamp L even after acknowledgement until depression of a manuallyoperable reset switch. Refer now to FIG. 7 which illustrates a minormodilication of the cir cuit of FIGS. 3 through 5 necessary to providenot only Va selection of lock-in and non-lock-in operation as the lattercircuit but also a selection of manual reset and automatic resetoperation. This modification includes the addition of a common reset bus300 connected through a normally open reset pushbutton switch 16 to thenegative voltage bus 28. The only additional change required is theaddition of a manual reset select switch 302 having two ganged levels30201 and 30212. The switch level 302a has a movable Contact 304connected to the upper terminal of the capacitor 212 associated with thereset input terminal 78 of the bistable circuit 4. The movable contactis adapted to make selective contact with two stationary contacts Nos. 1and 2. The contact No. 1 is connected to the asher bus 193 and isengaged by the movable contact 394 during automatic reset operation ofthe circuit. In such case, the annunciator circuit operates identical tothat described in connection with the annunciator system of FIGS. 3through 5. When the movable contact 304 is connected to stationarycontact No. 2, the circuit is adjusted for manual reset operationwherein the liasher circuit is decoupled from the capacitor 212 and theassociated circuit.

The second switch level 302!) is interposed between the resistor 211 andthe negative voltage bus 28 and the reset bus 300. The second level302]) has movable contact 306 engagable with stationary contacts Nos. 1and 2. For manual reset operation, movable contact 306 makes engagementwith contact No. 2 whichv in turn is connected to the reset bus 300.Contact No. 1 is connected to the negative voltage bus 2S so that whenthe movable contaot 306 connects with this terminal the operation of thesystem is identical to that previously described in connection with theannunciator system of FGS. 3 through 5. During manual reset operation,the lock-in control switch 206 must be connected to its contact No. 2which extends through the rectiiier 213 to the output 199 of thebistable circuit 4.

It will be recalled that reset of the first bistable circuitv 4 requiresfirst of all that the associated variablereturn to normal and that areset signal be fed to the control terminal 78 thereof. This resetsignal in the exemplary circuit described is a negative pulse. When themanual reset switch 302 is in the position No. 2 as illustrated and theswitch 206 is also in position for lock-in operation, a negative pulsecan be generated by momentarily operating the manual reset switch 16 tocouple the negative potential of the negative bus 28 through resistor211 to the capacitor 212. Prior to acknowledgement, it will be recalledthat the voltage at the output 199 of the bistable circuit 4' is atground or a relatively positive potential. This potential is coupledthrough rectifier 213 and the switch 206 to the upper plate of thecapacitor 212 to discharge and maintain discharged the capacitor 212.The discharge of the capacitor 212, as previously indicated, will resultin the generation of the positive pulse which has no effect on thebistable circuit 4 due to the blocking effect of rectifier 218. Afteracknowledgement, however, the potential at the output 199 of thebistable circuit 4 becomes negative, which negative potential is blockedby the rectifier 213. Then, operation of manual reset switch 16 will beeffective to couple the negative voltage to the capacitor 212 to effectthe charging thereof, resulting in generation of a negative pulse whichresets the bistable circuit 4.

The various aspects of applicants inventionhave thus provided a highlyunique and advantageous selection of standard annunciator systems. Mostpreferably, the static annunciator systems are transistorized systemscapable of operating from a relatively high direct current voltagedespite the low voltage ratings of the transistors. Moreover, due to theparticular circuit logic involved and the circuit connections forcarrying out this logic, an extremely fiexible and reliable staticannunciator results, even in the presence of fairly substantialdistributed capacitances in the line connecting the various fieldcontacts to their associated control circuits.

It should be understood that numerous modifications may be made of thevarious specific forms of the invention disclosed without deviating fromthe broader aspects of the invention.

What I claim as new and desire to protect by Letters' Patent of theUnited States is:

1. In an annunciator circuit for monitoring a number of variables andincluding for each variable alarm means for providing an alertindication, and variable responsive means having normal and abnormalconditions when the associated variable is respectively normal andabnormal, the improvement comprising a separate control circuitresponsive to each variable responsive means, means for controlling theassociated alarm means, each control circuit including: a first bistablecircuit having a first input terminal for receiving a control voltage ofa given polarity for setting the bistable circuit and a second inputterminal for receiving a control voltage of a given polarity whichresets the bistable circuit, means responsive to the setting andresetting of said bistable circuit for respectively energizing andde-energizingv said alarm means,` a source of said control voltage forsetting such first bistable circuit, means `connecting said source ofcontrol voltage continuously to said first input terminal when thecondition responsive means is in its abnormal condition, and la seriescircuit of a capacitor and a resistor connected across a source ofdirect current voltage, and means coupling the voltage developed acrosssaid resistor means to said second input of said bistable circuit andincluding rectifier means limiting the voltage coupled thereto apolarity which will reset the bistable control circuit; and a commonpulse bus and means for continuously pulsating said pulse bus with avoltage of a polarity which will discharge said capacitor in eachcontrol circuit, each of said capacitors normally recharging in theintervals between said pulses and the Charge current generating pulsesacross said resistor of a polarity to pass through said associatedrectifier means and reset the associated first bistable circuit if it isset, when the control voltage applied to the first input terminalthereof is removed.

2. In an annunciator circuit for monitoring a number of variables andincluding for each variable alarm means for providing an alertindication, variable responsive means having normal and abnormalconditions when the associated variable is respectively normal andabnormal, and manually operable reset switch means, the improvementcomprising a separate control circuit responsive to each variableresponsive means and said reset switch means for controlling theassociated alarm means, each control circuit including: a first bistablecircuit having a g first input terminal for receiving a control voltageof a given polarity for setting the bistable circuit and a second inputterminal for receiving a control voltage of a given polarity ,whichresets the bistable circuit, means responsive to the setting andresetting of said bistable circuit for respectively energizing andde-energizing said alarm means, a source of said control voltage forsetting such first bistable circuit, means connecting said source ofcontrol voltage continuously to said first input terminal when thecondition responsive means is in its abnormal condition, and a seriescircuit of a capacitor and a resistor connected across a source ofdirect current voltage, means coupling the voltage developed across saidresistor means to said second input of said bistable circuit andincluding rectifier means limiting the voltage coupled thereto apolarity which will reset the bistable control circuit, a common pulsebus and means for continuously pulsating said pulse bus with a voltageof a polarity which will discharge said capacitor in each controlcircuit, each of said capacitors normally recharging in the intervalsbetween said pulses and the charge current generating pulses acrosssaid. resistor of a polarity to pass through said associated rectifiermeans and reset the associated first bistable circuit if it is set, whenthe control voltage applied to the first input terminal thereof isremoved, each control circuit further including a second bistablecircuit having input terminal means for setting and resetting the sameand a reset inhibit output connected to said capacitor in therassociated control circuit for keeping the same discharged when thesecond bistable circuit is set and allowing the charge and dischargethereof when the second bistable circuit is reset, and a common busconnected through said manually operable reset switch means to a sourceof reset voltage for said second bistable circuits and feeding saidreset voltage to the second bistable circuits of said control circuitsto reset the same when the latter switch means is operated.

3. In an annunciator circuit'for monitoring a number of variables andincluding for each variable alarm means for providing an alertindication, v-ariable responsive means having normal and abnormalconditions when the associated variable is respectively normal andabnormal, and manually openable reset switch means, the improvementcomprising a separate control circuit responsive to each variableresponsive means and said reset switch means for controlling theassociated alarm means, each control circuit including: a first bistablecircuit having a first input terminal for receiving a control voltage ofa given polarity for setting the bistable circuit and a second inputterminal for receiving a control voltage of a given polarity whichresets the bistable circuit, means responsive to the setting andresetting of said bistable circuit for respectively energizing andde-energizing said alarm means, a source of said control voltage forsetting such first bistable circuit, means connecting said source ofcontrol voltage continuously to said first input terminal when thecondition responsive means isin its abnormal condition, a series circuitof a capacitor and a resistor connected across |a source of directcurrent voltage, means coupling the voltage developed across saidresistor means to said second input of said bistable circuit andincluding rectiiier means vlimiting the voltage coupled thereto apolarity which will reset the bistable control circuit; a common pulsebus and means for continuously pulsating said pulse bus with a voltageof a polarity which will discharge said capacitor in each controlcircuit, each of said capacitors normally recharging in the intervalsbetween said pulses and the charge current generating pulses across saidresistor of a polarity to pass through said associated rectiiier vmeansand reset the associated first bistable circuit if it is set, when thecontrol voltage applied to the tirst f input terminal thereof isremoved; each control circuit further including a second bistablecircuit having Vinput terminal means for setting and resetting the sameand a reset inhibit output connected to said capacitor in the associatedcontrol circuit for keeping the same discharged when the second bistablecircuit is set and allowing the charge and discharge thereof when thesecond bistable circuit is reset; a lock-in select switch forselectively cou-` pling and uncoupling the reset inhibit output of saidsecond bistable circuit to and from said capacitor to provide lock-in ornon-lock-in operation; land a common bus connected through saidmanuallyoperable reset switch means to a source of reset voltage forsaid second bistable circuits and feeding said reset voltage to thesecond bistable circuits of said control circuits to reset the same whenthe latter switch means is operated.

4. In an annunciator circuit including visual alarm means, variableresponsive means having normal and abnormal conditions when theassociated variable is respectively normal and abnormal, a source ofhigh direct current voltage, and manuallyv operable acknowledgmentswitch means, the improvementl comprising: a bistable transistor controlcircuit responsive to said variable Vresponsive means byproviding oneoutput condition when the associated variable is normal and anotheroutput condition when the associated variable is abnormal, a secondcontrol circuit responsive to the output conditions of said bistablecontrol circuit for controlling the energization of said alarm means,said bistable control circuit comprising: a pair of relatively lowvoltage transistor elements, said second control circuit comprising atleast one relatively high voltage transistor element, each of said`transistorelements having control and load terminals and designed foroperation with an applied voltage which is less than the value of the`output of said source of direct current voltage,l load resistor meansconnected in series between one of the load terminals of each of saidlow voltage transistor elements of said bistable control circuit andVsaid source of direct current voltage, feedback resistor means connectedbetween the load terminal of each of said low voltage transistor controlelements nearest said load resistor means and the control terminal ofthe other of same, controlV circuit resistor means connected between tthe control terminal of each of said low voltage transistorcontrol'element and the terminal of said source of direct i, currentvoltage which is remote from said load Vresistor means, each of saidload resistor means and the associated feedback and control circuitresistor means providing a voltage divider network to supply the properrelative low voltage conditions across the load terminals of theassociated low current transistor element, means connecting said alarmlight means in series between one of the load terminals of the highvoltage transistor element and said source of direct current voltage,shunt resistor means connected between the load terminals of said highvoltage transistor element and providing in conjunction with said alarmlight means the proper relative low voltage conditions across the loadterminals of said high voltage transistor element and a dim lightindication when the Vassociated variable is normal, meansr responsive tothe Output condition of said bistable control circuit indicatring anabnormal variable for periodically feeding at a visible ashing rate avoltage to the control terminal of t 1s! said high voltage transistorelement for effecting periodically a high conductive condition thereofto provide a llashing light indication on said alarm light means, and Ymeans responsive to momentary operation of said manually operableacknowledgement lmeans for providing steady voltage conditions on thecontrol terminal of the high voltage transistor element for continuouslyproviding a high conductivestate therein to provide a steady lightindication on the associated alarm light means.

5. In yan annunciator system for monitoring the condition of a number ofvariables, said system including visual alarm means and variableresponsive means for eachvariable having normal and abnormal conditionsvwhen the associated variablel is respectively normal and abnormal, acommon audible alarm means, a common source of signal pulses occurringat a visibleflashing rate,` and commonly manually-operableacknowledgement switch means, the improvement comprising an electricalcontrol circuit for each variable responsive to the associated variableresponsive means and said common acknowledgernent switch means forcontrolling said visual Vand audible alarm means, each `control circuitcomprising a first bistable unit having two states of operation, asecond t bistable unit having two states of operation, a tirst outputcontrolled by said second bistable unit and at which a gate-openingsignal-continuously appears only yas long as the bistable unit is in oneof its states of operationand Y a second output controlled bysaid-second bistable unit at which a gate-opening signal continuouslyappears only as long as said second bistable unit is in its other stateof operation, a rst and gate having irst and second control inputs forenergizing the associated visualialarmV v said rst and second and gatesonly as long as said first bistable unit remains set, means coupling thegate-opening signal at said tirstoutput controlled by said secondbistable unit to the iirst control input initially to energize saidcommon audible alarm means, a double or input connection coupled to therst control input means of said rst and gate and including aprst inputsection extending from said common source of signal pulses which providegate-opening signals at a visible flashing rate, to effect the visibleflashing of said visual alarm means when said first bistable unit isinitially set, and a secondinput section extending from said secondoutput controlled by said second bistable unit which provides acontinuousA gate-opening signal when the latter bistable unit is in saidone operating state, to provide aI steady light indication on saidvisualralarm means after acknowledgement,`

means responsive to the operation of said manually operableacknowledgement means for operating said second bistable unit Vfrom saidother to said one operating state whereby to provide a steady lightindication on said visual alarm means and to silence said audible alarm`means as the gate-'opening signals disappear from said rst outputcontrolled by said second bistable unit, and means for resetting theirst bistable unit after" the associated variable responsive meansreturns to its normal condition.

6. In an annunciator circuit for monitoring a number of variables andincluding for each variable alarm means for providing an alertindication, variable responsive means having normal and abnormalconditions when the associated variable is respectively normal andabnormal,`

and manually operable reset switch means, the improvement comprising aseparate control circuit responsive to each variable responsive meansand said reset switch means for controlling the associated alarm means,each control circuit including: a first bistable circuit having a firstinput terminal for receiving a control voltage of a given polarity forsetting the bistable circuit and a second input terminal for receiving acontrol voltage of a given polarity which resets the bistable circuit,means responsive to the setting and resetting of said bistable circuitfor respectively energizing and de-energizing said alarm means, a sourceof said control voltage for setting such iirst bistable circuit, meansconnecting said source of control voltage continuously to said firstinput terminal when the condition responsive means is in its abnormalcondition, and a series circuit of a capacitor and a resistor connectedacross a source of direct current voltage, means coupling thevoltagedeveloped across said resistor means to said second input of saidbistable circuit and including rectifier means limiting the voltagecoupled thereto to a polarity which will reset the bistable controlcircuit, a common pulse bus and means for continuously pulsating saidpulse bus with a voltage of a polarity which will discharge saidcapacitor in each control circuit, each of said capacitors normallyrecharging in the intervals between said pulses and the charge currentgenerating pulses across said resistor of a polarity to pass throughsaid associated rectifier means and reset the associated first bistablecircuit if it is set when the control voltage applied to the first inputterminal thereof is removed; and each control circuit further includinglock-in control means connected to said capacitor for keeping saidcapacitor discharged until operation of said reset switch means,whereupon the capacitor is free to charge and discharge until theassociated variable returns to normal and then becomes abnormal again.

' 7. In an annunciator system for monitoring the condition of a numberof variables, said system including visual alarm means and variableresponsive means for each variable, having abnormal and normalconditions when the associated variable is respectively normal andabnormal, a common source of signal pulses occurring at a visibleflashing rate, and common manually operable acknowledgement switchmeans, the improvement comprising an electrical control circuit for eachvariable responsive to the associated variable responsive means and saidcommon acknowledgement switch means for controlling said visual alarmmeans, each control circuit comprising: a first bistable unit havingseparate set and reset control input means, a second bistable unithaving control input means for setting and resetting the same,

a first output at which a gate-opening signal continuously appears onlyas long as the bistable unit is set, a second output at which a resetinhibit signal continuously appears only as long as said second bistableunit is reset, a first an gate having first and second control inputsfor energizing the associated visual alarm means when gate-openingsignals are simultaneously fed thereto, said pulses from said commonsource of pulses acting as gate-opening pulses, said first control meansresponsive to the operation of the associated variable responsive meansfor feeding a continuous set signal to the 'set control input means ofsaid first bistable unit which signal sets the same and preventsresetting thereof until removal of the set signal from the latter inputmeans, means responsive to the setting of said first bistable unit formomentarily feeding a set pulse to the second bistable unit for lsettingthe same and for continuously feeding a gate-opening to the secondcontrol input of said first and gates as long as said rst bistable unitremains set, a double or input connection coupled to the first controlinput means of said first and gate and including a first input sectionextending from said common source of signal pulses which providegate-opening signals at a visible flashing rate, to effect the visibleflashing of said visual alarm means when said first Vbistable unit isinitially set, and a second input section extending from said secondoutput of said second bistable unit which provides a continuousgate-opening signal when the latter bistable unit is reset, to provide asteady light indication on said visual alarm means afteracknowledgement, means responsive to the operation of said manuallyoperable acknowledgement means for feeding a reset signal to said secondbistable unit to reset the same whereby to provide a steady lightindication on said visual alarm means as the gate-opening signalsdisappear from said first output of said second bistable unit, a resetcircuit for said first bistable unit coupled to the reset control inputmeans of said first bistable unit, said reset circuit being coupled tosaid common source of pulses which act as reset pulses which normallycontinuously prepare said first bistable unit for a resetoperation whichis effected when the associated variable returns to normal, and meansconnecting said second output of said second bistable unit to which saidreset inhibit signal appears when the bistable unit is set, forinhibiting the coupling of the latter reset pulses to the reset controlinput means of said first bistable unit, to provide lock-in operationuntil the second bistable circuit is reset by said acknowledgernentswitch means.

8. ln an annunciator system for monitoring the condition of a number ofvariables, said system including visual alarmrmeans and Variableresponsive means for each variable having abnormal and normal conditionswhen the associated varible is respectively normal and abnormal, acommon source of signal pulses occurring at a visible flashing rate, anda common manually operable acknowledgement switch means,'the improvementcornprising an electrical control circuit for each variable responsiveto the associated variable responsive means and said commonacknowledgement switch means for controlling said visual alarm means,each control circuit comprising: a first bistable unit having separateset and reset control input means, a second bistable unit having controlinput means for setting and resetting the same, a first output at whicha gate-opening signal continuously appears only as long as the bistableunit is set, a second output at which a reset inhibit signalcontinuously appears only as long as said second bistable unit is reset,a iirst and gate having rst and second control inputs for energizing theassociated visual alarm means when gate-opening signals aresimultaneously fed thereto, said pulses from said common source ofpulses acting as gate-opening pulses, said first control meansresponsive to the operation of the associated variable responsive meansfor feeding a continuous set signal to the set ccntrol input means ofsaid first bistable unit which signal sets the same and preventsresetting thereof until removal of the set signal from the latter inputmeans, means responsive to the setting of said first bistable unit formomentarily feeding a set pulse to the second bistable unit for settingthe same and for continuously feeding a gate-opening to the secondcontrol input of said first and gates as long as said first bistableunit remains set, a double or input connection coupled to the rstcontrol input means of said first an gate and including a first inputsection extending from said common source of signal pulses which providegate-opening signals at a visible flashing rate, to effect the visibleflashing or said visual alarm means when said first bistable unit isinitially set, and a second input section extending from said secondoutput of said second bistable unit which provides a continuousgate-opening signal when the latter bistable unit is reset, to provide asteady light indication on said visual alarm means afteracknowledgement, means responsive to the operation of said manuallyoperable acknowledgement means for feeding a reset signal to saidsecondbistable runit to reset the same whereby to provide a steady lightindication on said visual alarm means as the gate-opening signalsdisappear 21 from said rst output of said second bistable unit, a resetcircuit for said rst bistable unit coupled to the reset control inputmeans of said rst bistable unit, said reset circuit being coupled tosaid common source of pulses which act as reset pulses which normallycontinuously prepare said rst bistable unit for a reset operation whichis effected when the associated variable returns to normal,V meansconnecting said second output of said second bistable unit to which saidreset inhibit signal appears When the bistable unit is set, forinhibiting the coupling of the latter reset pulses to the resetcontrolinput means of said rst bistable unit, to provide lock-inoperation until the second bistable circuit is reset by saidacknowledgement switch means, and manually operable switch means forselectively connecting and disconnecting the second output of saidsecond bistable unit to provide selectively for lock-n or non-lock-inoperation.

References Cited in the lile of this patent UNITED STATES PATENTS

2. IN AN ANNUCIATOR CIRCUIT FOR MONITORING A NUMBER OF VARIABLES ANDINCLUDING FOR EACH VARIABLE ALARM MEANS FOR PROVIDING AN ALERTINDICATION, VARIABLE RESPONSIVE MEANS HAVING NORMAL AND ABNORMALCONDITIONS WHEN THE ASSOCIATED VARIABLE IS RESPECTIVELY NORMAL ANDABNORMAL, AND MANUALLY OPERABLE RESET SWITCH MEANS, THE IMPROVEMENTCOMPRISING A SEPARATE CONTROL CIRCUIT RESPONSIVE TO EACH VARIABLERESPONSIVE MEANS AND SAID RESET SWITCH MEANS FOR CONTROLLING THEASSOCIATED ALARM MEANS, EACH CONTROL CIRCUIT INCLUDING: A FIRST BISTABLECIRCUIT HAVING A FIRST INPUT TERMINAL FOR RECEIVING A CONTROL VOLTAGE OFA GIVEN POLARITY FOR SETTING THE BISTABLE CIRCUIT AND A SECOND INPUTTERMINAL FOR RECEIVING A CONTROL VOLTAGE OF A GIVEN POLARITY WHICHRESETS THE BISTABLE CIRCUIT, MEANS RESPONSIVE TO THE SETTING ANDRESETTING OF SAID BISTABLE CIRCUIT FOR RESPECTIVELY ENERGIZING ANDDE-ENERGIZING SAID ALARM MEANS, A SOURCE OF SAID CONTROL VOLTAGE FORSETTING SUCH FIRST BISTABLE CIRCUIT, MEANS CONNECTING SAID SOURCE OFCONTROL VOLTAGE CONTINUOUSLY TO SAID FIRST INPUT TERMINAL WHEN THECONDITION RESPONSIVE MEANS IS IN ITS ABNORMAL CONDITION, AND A SERIESCIRCUIT OF A CAPACITOR AND A RESISTOR CONNECTED ACROSS A SOURCE OFDIRECT CURRENT VOLTAGE, MEANS COUPLING THE VOLTAGE DEVELOPED ACROSS SAIDRESISTOR MEANS TO SAID SECOND INPUT OF SAID BISTABLE CIRCUIT ANDINCLUDING RECTIFIER MEANS LIMITING THE VOLTAGE COUPLED THERETO APOLARITY WHICH WILL RESET THE BISTABLE CONTROL CIRCUIT, A COMMON PULSEBUS AND MEANS FOR CONTINUOUSLY PULSATING SAID PULSE BUS WITH A VOLTAGEOF A POLARITY WHICH WILL DISCHARGE SAID CAPACITOR IN EACH CONTROLCIRCUIT, EACH OF SAID CAPACITORS NORMALLY RECHARGING IN THE INTERVALSBETWEEN SAID PULSES AND THE CHARGE CURRENT GENERATING PULSES ACROSS SAIDRESISTOR OF A POLARITY TO PASS THROUGH SAID ASSOCIATED RECTIFIER MEANSAND RESET THE ASSOCIATED FIRST BISTABLE CIRCUIT IF IT IS SET, WHEN THECONTROL VOLTAGE APPLIED TO THE FIRST INPUT TERMINAL THEREOF IS REMOVED,EACH CONTROL CIRCUIT FURTHER INCLUDING A SECOND BISTABLE CIRCUIT HAVINGINPUT TERMINAL MEANS FOR SETTING AND RESETTING THE SAME AND A RESETINHIBIT OUTPUT CONNECTED TO SAID CAPACITOR IN THE ASSOCIATED CONTROLCIRCUIT FOR KEEPING THE SAME DISCHARGED WHEN THE SECOND BISTABLE CIRCUITIS SET AND ALLOWING THE CHARGE AND DISCHARGE THEREOF WHEN THE SECONDBISTABLE CIRCUIT IS RESET, AND A COMMON BUS CONNECTED THROUGH SAIDMANUALLY OPERABLE RESET SWITCH MEANS TO A SOURCE OF RESET VOLTAGE FORSAID SECOND BISTABLE CIRCUITS AND FEEDING SAID RESET VOLTAGE TO THESECOND BISTABLE CIRCUITS OF SAID CONTROL CIRCUITS TO RESET THE SAME WHENTHE LATTER SWITCH MEANS IS OPERATED.